This invention relates to the digital communication art and, more particularly, to a means for reducing the length of a transmission bit stream by combining sync bits with data bits.
Digitally encoded communication systems are well known in the art. In such systems, a data bit stream containing digitally encoded information is to be transmitted over a noisy transmission medium. If the raw information data were transmitted without being processed, there would exist a substantial probability that portions of the message might be lost due to interference from the noisy medium. Therefore, this data is normally processed to produce a transmission bit stream, which, after decoding at the receiver provides a means to correct or minimize transmission medium induced errors. Two examples of error correction processing schemes are block and convolutional type codes.
Proper decoding of the transmission bit stream requires that the decoder be able to recognize and synchronize with the received bit stream signal. To assure proper decoding synchronization, the prior art has utilized a predetermined set of N sync bits preceding the M data bits, as is illustrated in FIG. 1. The N sync bits follow a pattern, such as the well known Barker sequence, which optimizes the ability of the decoder to recognize and synchronize with the transmission bit stream.
A problem with the aforementioned prior art synchronization schemes is that the transmission bit stream has a minimum bit length of M+ N. In some systems, the number N of sync bits must be substantial with respect to the number of M data bits to assure the desired probability of synchronization whereby the overall message length is quite long, thus requiring a lengthy transmission time. It is, of course, desirable to reduce transmission time to an absolute minimum.